In radiographic laser printers, an unexposed radiographic film sheet is removed from a stack of film sheets and transported to an exposure station where it is exposed by a laser to a radiographic image. The unexposed film sheets are contained in a light tight magazine or cartridge which is opened when a film sheet is to be removed.
A known film sheet picker mechanism includes several vacuum cups mounted on a rigid manifold which is rotatably mounted at the end of a movable picker arm. A linkage driven by a standard electrical solenoid positions the vacuum cups in a manner that allows their perimeter to make full contact with the surface of the top film sheet. When the electrical power to the solenoid is removed a spring moves the vacuum cups in a manner that enhances the ability of the top sheet of film to separate itself from the sheet immediately below. The picker mechanism also incorporates a top of film detector designed to alert the mechanism's control system that the vacuum cups are near the top surface of the top film in a stack. Electrical conductors connect both the solenoid and detector to the support frame for the picker mechanism.
Such a picker assembly has several disadvantages.
1. The solenoid electrical conductors and the linkage connecting the solenoid to the vacuum cups frequently fail in a catastrophic manner which can result in a total machine shut down and an untimely and costly repair. PA1 2. The solenoid, its linkage and associated electrical circuits are complex, expensive and unreliable. PA1 3. The electrical wiring connecting the top of film sensor to the control electronics can fail due to abrasion and numerous flexures during normal operation. The consequent failure of the top of film detector can result in a destructive collision between the film picking mechanism and the top surface of the film. PA1 1. The elimination of the known solenoid, linkage, and connecting electrical wiring results in a robust design having long life and low repair cost. PA1 2. The unit manufacturing cost and complexity is substantially reduced while eliminating several potential causes of failure. PA1 3. Frequent failures caused by flexing electrical conductors connected to a sensor mounted to a rotating lever are eliminated. PA1 4. Elimination of the top of film detector from the moving picker mechanism eliminates the possibility of failures to detect the presence of film due to broken wires that have fatigued during normal usage.
There is thus a need for a film sheet picker mechanism which solves these problems.